'Follow Active Quads" not working?
EDIT

If you are using an array modifier the mesh of your object is sill only one plane that is repeated along a curve. The follow active quads will not work until you apply the modifier: only then your mesh will be a sereis of connected planes.

Once you do that then you can do proper unwrapping.

First select just one face.

Select then all of the faces (press A).

You'll see that the face you had selected first is marked as active (with a dotted pattern)

Then do unwrap (U) Follow Active Quads.